1. Field of the Invention
The present invention relates to an ink jet recording apparatus for forming a record by discharging ink from recording means to a recording material.
2. Related Background Art
Recording apparatus constructed as a printer, a copying machine or a facsimile, or employed as the output unit for a work station or an integral electronic equipment including a computer or a word process, is designed to record an image on a recording material (recording medium) such as paper or a plastic sheet. Such recording apparatus can be classified, by the recording system, for example as ink jet printers, wire dot printers, thermal printers, laser beam printers etc.
In the recording apparatus of the serial scanning type, in which main scanning is conducted in a direction perpendicular to the transporting direction (sub scanning direction) of the recording material, the recording thereon is achieved, after said recording material is set in a predetermined recording position, by repeating the operations of recording a line image with recording means (generally supported by a carriage) moving along said recording material (main scanning operation), advancing the recording material by a predetermined amount (transportation of recording material), and recording the image of a next line on the recording material when it is stopped again. On the other hand, in the recording apparatus of the line type in which the recording is achieved solely by sub scanning in the transporting direction of the recording material, the recording thereon is achieved, after the recording material is set in a predetermined recording position, by repeating the operations of collectively recording a line image, then advancing the recording material by a predetermined amount, and collectively recording the next line.
Among various recording apparatus mentioned above, an ink jet recording apparatus, forming a record by discharging ink from recording means (recording head) onto a recording material, has the advantages of easy size reduction of the recording means, capability of high-speed recording of a fine image and for recording on plain paper without any special treatment, low running cost, low noise level because of non-impact recording, and easy recording of a color image with inks of plural colors. Particularly a line-type apparatus, employing line-type recording means, having an array of plural discharge openings along the transverse direction of the recording material, can attain a higher recording speed.
In particular, an ink jet recording head utilizing thermal energy for ink discharge can be manufactured with a higher density of discharge openings, by the formation of electrothermal converters, electrodes, liquid path walls, cover plates etc. on a substrate, utilizing the steps common in the semiconductor process, such as etching, evaporation sputtering etc., whereby further compactization can be realized. Also various requirements exist for the materials used for the recording medium, and it is recently desired to form recording not only on ordinary paper and plastic sheet (for overhead projectors, but also on thin paper and worked paper such as punched paper for filing, paper with roulette holes, paper of arbitrary size etc.
Such ink jet recording apparatus employs, for maintaining a proper discharge state of the recording head or restoring the proper discharge state in case the discharge openings of said head are clogged, recovery means involving a recovery pump for sucking ink out of the discharge openings by a negative pressure generated by said pump. A tube pump, generating a negative pressure by a volume change in a flexible tube, is often utilized as such a recovery pump and has the advantages of a simple structure, a low cost, a small size and a light weight.
FIGS. 17 and 18 are vertical cross-sectional views of a conventional tube pump, respectively at the start and end of tube pinching. On a discharge opening face 51 of a recording head 1, the aperture of a cap 2 is maintained in contact to seal a discharge opening 52. On a rear aperture of the cap 2, there is connected a tube 3 which extends to the tube pump 4. Said tube pump 4 is composed of a pump base 5, rotatably supporting a guide roller 6, which in turn rotatably supports a pressure roller 7. In more details, a shaft 8 of the pressure roller 7, for pressing the tube 3, is rotatably supported by the guide roller 6, of which shaft 9 is rotatably supported by the pump base 5. The pump base 5 is provided with an arc-shaped groove 10, concentric with the shaft 9 of the guide roller 6, for accommodating the tube 3. At the other end, at the downstream side, of the tube 3, there is provided a used tank reservoir 11 for storing the ink sucked from the discharge opening 52.
When the guide roller 6 is rotated in a direction a by drive means (not shown), the pressure roller 7 provided on the guide roller 6 comes into contact with the tube 3 at a position X shown in FIG. 17, thereby pressing the tube 3 until the internal space thereof at the pressed portion becomes zero. When the guide roller 6 is further rotated in said direction a from this state, the pressure roller 7 effects rotation in a direction b while continuously pressing the tube 3 and making revolution in the direction a. The pump temporarily stops when the pressure roller 7 reaches a position Y shown in FIG. 18, and the negative pressure, generated by the volume change in the tube 3 based on the pressing by the roller 7 between the positions X and Y acts on the discharge opening 52 of the recording head 1, thus sucking the ink out of said opening. The sucked ink is forwarded in succession to said used ink reservoir 11.
In case plural recording heads 1 are employed, as in a color ink jet recording apparatus, there are provided plural tubes 3 corresponding to the number of the recording heads 1, and the guide roller 6 is given plural pressure rollers 7 corresponding to the number of said tubes 3. In the conventional ink jet recording apparatus with plural recording heads, in order to provide said recording heads with a same suction force, the distances from the recording head 1 to the X and Y positions have to be same for every tube 3, and the pressure roller 7 has to be mounted on the guide roller 6 so as to come into contact with and to detach from the tube 3 at a same timing.
In such conventional configuration, however, in case the motor for the pump is also used for paper advancement or for carriage drive for the purpose of compactization or cost reduction of the entire apparatus, there may result a synchronization failure in the motor, an instability in the precision of paper advancement or an unevenness in the recorded image in the scanning direction of the carriage, leading to the deterioration of the recorded image quality, due to a torque fluctuation generated at the moment when the pressure roller 7 presses the tube 3 or is released therefrom.
Also in the conventional configuration, the pressure rollers 7 press the tubes 3 at a same timing. However, since the torque required for pump driving becomes largest at the moment when the pressure roller 7 starts to press the tube 3, the pump driving maximum torque increases at such moment in proportion to the increase of the number of the tubes 3 and the pressure rollers 7, whereby there is required a larger motor with an increased cost.
Furthermore, in the above-explained conventional configuration, the pump may be driven by a driving power source for other purpose, such as for transporting the recording material, used both in the forward and reverse directions. In case the guide roller 6 shown in FIG. 17 is reversed in a direction f, and if ink discharged from the recording head 1 by suction in the forward driving and not having reached the used ink reservoir 11 remains in the tube 3, said ink flows inversely toward the cap 2, thus overflowing therefrom, or sticking onto the discharge opening face of the head or mixing with the ink in said discharge opening, thus eventually inducing recording failure.
In order to avoid such drawback, there is conceived a method of rotating, after the sucking operation, the guide roller 6 in the direction a in the uncapped state, in order to move the sucked ink toward the used ink reservoir 11 as much as possible. However, if said reservoir 11 is distant from the tube pump 4, the guide roller 6 has to be rotated considerably in the direction a, so that the recovery operation becomes very long. On the other hand, said reverse flow of ink can be avoided by employing an exclusive driving power source, rotating only in direction, for the tube pump 4, but such method elevates the cost and increases the volume of the apparatus.